The average UK viewer watched just three minutes a day of television off the main set in 2012, according to an industry report.
By contrast, people watched on average four hours and one minute of linear programming on the TV set a day, marking the fourth straight year that daily viewing has remained above four hours.
Using 2012 data supplied by Broadcasters' Audience Research Board (BARB) and the broadcasters themselves, commercial TV marketing body Thinkbox produced what is claimed to be the first "platform-neutral total TV viewing figures".
Viewers were found on average to watch three 30-minute episodes a month on non-TV devices, such as tablets, smartphones and laptops.
It was revealed that most 'off-TV' viewing is on-demand and via established services such as ITV Player, Sky Go, 4oD and BBC iPlayer, although there is also some live streaming of content online.
Overall, smartphones, laptops and tablets account for 1.2% of additional TV consumption.
The average viewer watched four hours and one minute of linear TV a day in 2012, compared to four hours and two minutes in 2011, according to BARB.
But Thinkbox managing director Lindsey Clay said that linear TV is "the bedrock of how we watch TV and that is not going to change".
She added: "Its continued strength underlines viewers' preference for watching TV as it is broadcast and on a TV set.
"Viewing via personal devices, which we have been able to estimate for the first time, is in comparison relatively small, but it is growing rapidly and helping TV as a whole to expand.
"This is great for viewers who can watch what they want, when they want; and great for advertisers for whom TV - the biggest digital medium - is expanding."
Also in the Thinkbox report, it was revealed that 51% of UK households owned a digital TV recorder, such as Sky+ or Freeview+, in 2012, compared to 50% in the previous year.
But BARB figures suggest the growth in timeshifted viewing is slowing. In 2010, 7.6% of TV viewing was timeshifted, and that jumped to 9.4% in 2011. However, there was a much smaller increase in 2012, to 10.1%.
Thinkbox commented: "Once all households have the ability to digitally record TV programmes, Thinkbox expects the average level of recorded and playback TV viewing to settle at around 15% of total linear viewing, as it has in those households that do currently own DTRs. However on-demand TV will increase as a proportion of the time-shifted total."